(U) NAVSTAR Global Positioning System(GPS) Block IIR

(The effects of any budget/program decisions made since the information was collected during 1997-98 are NOT reflected in the National Security Space Road Map (NSSRM).)

Overview: (U)
(U)  NAVSTAR Global Positioning System (GPS) is a satellite-based radio positioning/navigation (POS/NAV) system that provides extremely accurate, three dimensional, common grid position, velocity and time of day information to users anywhere on or near the earth.  The system uses a constellation of 24 satellites which provides navigation data to both military and civilian users worldwide. The system provides reliable and accurate passive worldwide positioning, navigation, and timing information in all weather conditions, in real time, using a common grid reference system.  

(U)  The BLOCK IIR satellites, SVNs 41 through 62, are the operational replenishment satellites developed by General Electric (now Lockheed Martin) and will carry the GPS well into the next century.

Description: (U)
(U)  The Space Segment is an earth-orbiting constellation of 24 NAVSTAR satellites in six planes. The nominal circular orbit has a  20,200 kilometer (10,900 nautical mile) altitude and the orbits are inclined at an angle of 55 degrees with a 12-hour period. The spacing of satellites in their orbital planes are arranged such that a minimum of four satellites will be in view everywhere on and near the surface of the earth at any time. Each NAVSTAR satellite is designed to broadcast a pair of L-band radio frequency (RF) signals, known as Link 1 (L1 = 1575.42 MHz) and Link 2 (L2 = 1227.6 MHz). The L1 signal carries a precision ranging code and coarse / acquisition code,  while L2 carries only the precise ranging code. The signals are broadcast using spread spectrum techniques, employing two different spreading functions: a 1.023 MHz coarse / acquisition (C/A) code on L1 only and a 10.23 MHz precision (P) code on both L1 and L2. The minimum signal power for the different signals at a GPS receiver are: L1 C/A = -160 dBW; L1 P = -163 dBW; and for L2 P = -166 dBW. Superimposed on these codes are low-rate navigation message data, including satellite clock and ephemeris parameters, satellite signal health data, and Coordinated Universal Time (UTC) synchronization information. 

(U)  In 1989, the Block IIR procurement began for 21 additional satellites ("replenishment SVs") from Lockheed Martin, formerly General Electric.  The Block IIR SVs will present an identical SIS interface to the User Segment. Under a survivability scenario, the Block IIR SVs will have the capabilities to autonomously navigate  (AUTONAV) themselves and generate their own 50 Hz navigation message data. These AUTONAV capabilities will enable the Block IIR SVs to maintain full SIS accuracy for at least 180 days without Control Segment support. AUTONAV will also significantly improve both the reliability and integrity of the broadcast SIS. Accuracy improvements are expected to be approximately 7 meters spherical error probable (SEP) in a full Block IIR constellation. Additional differences between IIR and IIA are: 

(U) NAVIGATION PAYLOAD 
 -- (U)  additional radiation hardening 
 -- (U)  cross link ranging 
 -- (U)  reprogrammable micro-processor 
 -- (U)  two atomic clocks on at all times (hot backup) 
(U)  ELECTRICAL POWER SYSTEMS (EPS) 
 -- (U)  3 Ni CAD to 2 NiH batteries 
(U)  ATTITUDE AND VELOCITY CONTROL SYSTEMS (AVCS) 
 -- (U)  manual acquisition/pointing to autonomous 
(U)  SYSTEM DESIGN 
 -- (U)  larger fuel capacity 
 -- (U)  redundancy management system in SV processor 

(U)  The Block IIR satellites will be launched as needed to replace existing Block IIA satellites in order to sustain a 24 satellite constellation.

(U)  The GPS control or ground segment consists of five unmanned monitor stations located around the world (Hawaii; Kwajalein in the Pacific Ocean; Diego Garcia in the Indian Ocean; Ascension Island in the Atlantic Ocean; and Colorado Springs, Colorado); a master ground station at Schriever Air Force Base in Colorado Springs, Colorado; and four large ground antenna stations that broadcast signals to the satellites. The stations also track and monitor the GPS satellites.

User Impact: (U)
(U)  GPS provides an all-weather, global, protected (encrypted) navigation signal to all DoD users and allies.  The signal provides positioning accuracy's to about 7m 50 percentile spherical error probable and a timing signal for DoD communications and command and control systems to a precision of <100ns dual root mean square.  GPS receivers vary in capability and performance but are being integrated into many operational systems at costs under $3,000/platform. 

Programmatics: (U)
(U) Operational/Programmed.
	(U) IOC: 09/1997 (4QFY1997).
		(U) First Block IIR Delivery:  3QFY96.
(U) First Block IIR Launch:  3QFY97.
	(U) FOC: 09/2002 (4QFY2002).
		(U)  TBR: 4QFY2002 represents the last Block IIR launch.
	(U) Termination: 01/2012 (2QFY2012).
		(U)  The 01/01/2012 termination date is an approximate date used to show the follow-on relationship between NAVSTAR GPS Block IIR and NAVSTAR GPS Block IIF.   Block IIR satellites will gradually be replaced by Block IIF satellites between 2002 and 2012.  PE35165F.

Related Initiatives: (U)
(U) 3A Airborne Receiver, 3S Shipborne Receiver, Arnold Engineer Dev Cntr (AEDC), Combat Survivor Evader Locator, CRPA/AE-1, Defense Advanced GPS Receiver, Delta II, Eastern Range, Embedded GPS Inertial Nav. Sys., FRPA./AE-4, GAS-1 CRPA/AE, GPS Block IIA, GPS Block IIF, GPS Receiver Applications Module, GPS VME Receiver Card (GVRC), Miniature Airborne GPS Rec. 2000, Miniaturized Airborne GPS Rec., Precision Lightweight GPS Rec.

Related Requirements: (U)
(U) None.

Related Categories: (U)
(U) Navigation, Satellite Operations, Space Systems, Space-Based Warning

Road Map Placements: (U)
(U) Major DoD Space Programs, National Security Space Road Map, NAVIGATION.

Lead Office: (U)
(U) Air Force.

Date of Information: (U)
01 November 1997

(The effects of any budget/program decisions made since the information was collected during 1997-98 are NOT reflected in the National Security Space Road Map (NSSRM).)